A nano‐delivery system expands the insecticidal target of thiamethoxam to include a devastating pest, the fall armyworm

Abstract

Nano-delivery systems have been applied to deliver various synthetic/botanical pesticides to increase the efficiency of pesticide use and reduce the volumes of pesticides applied. Previous studies have supported the hypothesis that the nanocarriers can help expand the insecticidal target of pesticides to include non-target pests. However, the potential mechanism underlying this interesting phenomenon remains unclear. Herein, a widely applied star polycation (SPc) nanocarrier was synthesized to construct a thiamethoxam (TMX) nano-delivery system. The SPc-based delivery system could promote the translocation of exogenous substances across the membrane of Sf9 cells, increase the cytotoxicity of TMX against Sf9 cells by nearly 20%, and expand the insecticidal target of TMX to include Spodoptera frugiperda (the fall armyworm), with a 27.5% mortality increase at a concentration of 0.25 mg/mL. Moreover, the RNA-seq analysis demonstrated that the SPc could upregulate various transport-related genes, such as Rab, SORT1, CYTH, and PIKfyve, for the enhanced cellular uptake of TMX. Furthermore, enhanced cell death in larvae treated with the TMX-SPc complex was observed through changes in the expression levels of death-related genes, such as Casp7, BIRC5, MSK1, and PGAM5. The SPc-based nano-delivery system improved the cellular uptake of TMX and expanded its insecticidal target by adjusting the expression levels of death-related genes. The current study mainly identified the transport and cell death genes related to nanocarrier-based insecticidal target expansion, which is beneficial for understanding the bioactivity enhancement of the nano-delivery system.

A Nano-Delivery System Enhances the Stomach Toxicity of Methoxyfenozide against Spodoptera litura by Suppressing the Synthesis of Insect Cuticle Protein

“…The stomach toxicity of the methoxyfenozide/SPc complex was evaluated using second instar larvae of S. litura through the oral feeding method as described by Jiang et al Pure methoxyfenozide was dissolved in acetone and then mixed with SPc at the mass ratio of 1:2.06 according to PLC. The formulations (200 μL) including methoxyfenozide (0.3 mg/mL), methoxyfenozide/SPc complex (0.3 mg/mL), SPc (0.62 mg/mL), and ddH 2 O (Control) were added in the artificial diet (1 g).…”

“…The current result was consistent with a previous study that SPc can improve the bioactivity of thiamethoxam by 31.57%, avermectin by 74.35%, and dinotefuran by 26.82%. 14,17,48 The possible explanation for enhanced toxicity could be the pesticide nanometerization by the nano-delivery system, which increased the contact area of pesticides. Moreover, the nanocarrier facilitated cellular endocytosis and exocytosis processes to promote the cellular uptake of pesticide.…”

“…The SPc can assemble with various synthetic/botanical pesticides to reduce their particle size and increase their water dispersity, which, in turn, improves the plant/cellular uptake and their efficacy in controlling various plant diseases and pests. For instance, the complexation with SPc can decrease the particle sizes of osthole, matrine, dinotefuran, etc., down to nanoscale. − The nanoscale pesticide/SPc complex can penetrate the insect cuticle or plant cell wall and activate the clathrin-mediated endocytosis for enhanced cellular uptake. − SPc-loaded pesticides exhibit stronger bioactivity toward various plant diseases and pests such as western flower thrips, strawberry powdery mildew, green peach aphids, two-spotted spider mites, etc. , Recently, a publication reports that the SPc can codeliver pesticide and double-stranded RNA targeting insect key genes to achieve highly efficient pest management . Although the extremely high concentration of SPc can induce strong immune responses of insects, the SPc at working concentration exhibits negligible biotoxicity. , Thus, the SPc is an efficient and safe nanocarrier/adjuvant for pesticides with a broad application area.…”

Star Polymer-Based Nanodelivery System for Pesticides: Enhanced Broad-Spectrum Toxicity and Selective Toxicity

“…As shown in Table 1, the PLC of SPc toward spirotetramat was examined using the freeze-drying method, and it was calculated to be 36.16%, which was comparable to methoxyfenozide (32.66%) and higher than dinotefuran (17.41%) and thiamethoxam (20.63%). 19,21,23 High PLC also revealed the successful assembly of SPc with spirotetramat, and their dominant interaction force was examined using ITC (Figure 1). According to the previous interpretation of ITC data, 38 the high affinity constant Ka (6.420 × 10 4 M −1 ) suggested a strong interaction between SPc and spirotetramat.…”

“…21 Furthermore, the SPc-based nanodelivery system can expand the insecticidal target of thiamethoxam toward fall armyworms. 46 As expected, the application of SPc at the highest concentration exhibited no lethal effects on the two insect species. A previous study has examined the potential negative effects of SPc on model insect Drosophila melanogaster.…”